Classical Conditioning of Metallothionein Synthesis in Mice

To clarify the role of metallothionein (MT), an antistress protein, induced by psychological stress, we carried out an experiment to determine whether hepatic MT synthesis induced by restraint stress can be classically conditioned by an olfactory odor cue of camphor. Mice were conditioned by exposure to the odor of camphor 1 hr before restraint stress and partly during restraint stress. Although exposure to the odor of camphor did not elevate hepatic MT levels in itself, the odor stimuli significantly elevated hepatic MT levels in mice conditioned for 3 days. The results indicate that MT synthesis is induced by an association of the central nervous system with psychological stress.